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diff --git a/examples/widgets/doc/stardelegate.qdoc b/examples/widgets/doc/stardelegate.qdoc new file mode 100644 index 0000000000..aba8864c2b --- /dev/null +++ b/examples/widgets/doc/stardelegate.qdoc @@ -0,0 +1,296 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/ +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of +** this file. +** +** Other Usage +** Alternatively, this file may be used in accordance with the terms +** and conditions contained in a signed written agreement between you +** and Nokia. +** +** +** +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example itemviews/stardelegate + \title Star Delegate Example + + The Star Delegate example shows how to create a delegate that + can paint itself and that supports editing. + + \image stardelegate.png The Star Delegate Example + + When displaying data in a QListView, QTableView, or QTreeView, + the individual items are drawn by a + \l{Delegate Classes}{delegate}. Also, when the user starts + editing an item (e.g., by double-clicking the item), the delegate + provides an editor widget that is placed on top of the item while + editing takes place. + + Delegates are subclasses of QAbstractItemDelegate. Qt provides + QItemDelegate, which inherits QAbstractItemDelegate and handles + the most common data types (notably \c int and QString). If we + need to support custom data types, or want to customize the + rendering or the editing for existing data types, we can subclass + QAbstractItemDelegate or QItemDelegate. See \l{Delegate Classes} + for more information about delegates, and \l{Model/View + Programming} if you need a high-level introduction to Qt's + model/view architecture (including delegates). + + In this example, we will see how to implement a custom delegate + to render and edit a "star rating" data type, which can store + values such as "1 out of 5 stars". + + The example consists of the following classes: + + \list + \li \c StarRating is the custom data type. It stores a rating + expressed as stars, such as "2 out of 5 stars" or "5 out of + 6 stars". + + \li \c StarDelegate inherits QItemDelegate and provides support + for \c StarRating (in addition to the data types already + handled by QItemDelegate). + + \li \c StarEditor inherits QWidget and is used by \c StarDelegate + to let the user edit a star rating using the mouse. + \endlist + + To show the \c StarDelegate in action, we will fill a + QTableWidget with some data and install the delegate on it. + + \section1 StarDelegate Class Definition + + Here's the definition of the \c StarDelegate class: + + \snippet itemviews/stardelegate/stardelegate.h 0 + + All public functions are reimplemented virtual functions from + QItemDelegate to provide custom rendering and editing. + + \section1 StarDelegate Class Implementation + + The \l{QAbstractItemDelegate::}{paint()} function is + reimplemented from QItemDelegate and is called whenever the view + needs to repaint an item: + + \snippet itemviews/stardelegate/stardelegate.cpp 0 + + The function is invoked once for each item, represented by a + QModelIndex object from the model. If the data stored in the item + is a \c StarRating, we paint it ourselves; otherwise, we let + QItemDelegate paint it for us. This ensures that the \c + StarDelegate can handle the most common data types. + + In the case where the item is a \c StarRating, we draw the + background if the item is selected, and we draw the item using \c + StarRating::paint(), which we will review later. + + \c{StartRating}s can be stored in a QVariant thanks to the + Q_DECLARE_METATYPE() macro appearing in \c starrating.h. More on + this later. + + The \l{QAbstractItemDelegate::}{createEditor()} function is + called when the user starts editing an item: + + \snippet itemviews/stardelegate/stardelegate.cpp 2 + + If the item is a \c StarRating, we create a \c StarEditor and + connect its \c editingFinished() signal to our \c + commitAndCloseEditor() slot, so we can update the model when the + editor closes. + + Here's the implementation of \c commitAndCloseEditor(): + + \snippet itemviews/stardelegate/stardelegate.cpp 5 + + When the user is done editing, we emit + \l{QAbstractItemDelegate::}{commitData()} and + \l{QAbstractItemDelegate::}{closeEditor()} (both declared in + QAbstractItemDelegate), to tell the model that there is edited + data and to inform the view that the editor is no longer needed. + + The \l{QAbstractItemDelegate::}{setEditorData()} function is + called when an editor is created to initialize it with data + from the model: + + \snippet itemviews/stardelegate/stardelegate.cpp 3 + + We simply call \c setStarRating() on the editor. + + The \l{QAbstractItemDelegate::}{setModelData()} function is + called when editing is finished, to commit data from the editor + to the model: + + \snippet itemviews/stardelegate/stardelegate.cpp 4 + + The \c sizeHint() function returns an item's preferred size: + + \snippet itemviews/stardelegate/stardelegate.cpp 1 + + We simply forward the call to \c StarRating. + + \section1 StarEditor Class Definition + + The \c StarEditor class was used when implementing \c + StarDelegate. Here's the class definition: + + \snippet itemviews/stardelegate/stareditor.h 0 + + The class lets the user edit a \c StarRating by moving the mouse + over the editor. It emits the \c editingFinished() signal when + the user clicks on the editor. + + The protected functions are reimplemented from QWidget to handle + mouse and paint events. The private function \c starAtPosition() + is a helper function that returns the number of the star under + the mouse pointer. + + \section1 StarEditor Class Implementation + + Let's start with the constructor: + + \snippet itemviews/stardelegate/stareditor.cpp 0 + + We enable \l{QWidget::setMouseTracking()}{mouse tracking} on the + widget so we can follow the cursor even when the user doesn't + hold down any mouse button. We also turn on QWidget's + \l{QWidget::autoFillBackground}{auto-fill background} feature to + obtain an opaque background. (Without the call, the view's + background would shine through the editor.) + + The \l{QWidget::}{paintEvent()} function is reimplemented from + QWidget: + + \snippet itemviews/stardelegate/stareditor.cpp 1 + + We simply call \c StarRating::paint() to draw the stars, just + like we did when implementing \c StarDelegate. + + \snippet itemviews/stardelegate/stareditor.cpp 2 + + In the mouse event handler, we call \c setStarCount() on the + private data member \c myStarRating to reflect the current cursor + position, and we call QWidget::update() to force a repaint. + + \snippet itemviews/stardelegate/stareditor.cpp 3 + + When the user releases a mouse button, we simply emit the \c + editingFinished() signal. + + \snippet itemviews/stardelegate/stareditor.cpp 4 + + The \c starAtPosition() function uses basic linear algebra to + find out which star is under the cursor. + + \section1 StarRating Class Definition + + \snippet itemviews/stardelegate/starrating.h 0 + \codeline + \snippet itemviews/stardelegate/starrating.h 1 + + The \c StarRating class represents a rating as a number of stars. + In addition to holding the data, it is also capable of painting + the stars on a QPaintDevice, which in this example is either a + view or an editor. The \c myStarCount member variable stores the + current rating, and \c myMaxStarCount stores the highest possible + rating (typically 5). + + The Q_DECLARE_METATYPE() macro makes the type \c StarRating known + to QVariant, making it possible to store \c StarRating values in + QVariant. + + \section1 StarRating Class Implementation + + The constructor initializes \c myStarCount and \c myMaxStarCount, + and sets up the polygons used to draw stars and diamonds: + + \snippet itemviews/stardelegate/starrating.cpp 0 + + The \c paint() function paints the stars in this \c StarRating + object on a paint device: + + \snippet itemviews/stardelegate/starrating.cpp 2 + + We first set the pen and brush we will use for painting. The \c + mode parameter can be either \c Editable or \c ReadOnly. If \c + mode is editable, we use the \l{QPalette::}{Highlight} color + instead of the \l{QPalette::}{Foreground} color to draw the + stars. + + Then we draw the stars. If we are in \c Edit mode, we paint + diamonds in place of stars if the rating is less than the highest + rating. + + The \c sizeHint() function returns the preferred size for an area + to paint the stars on: + + \snippet itemviews/stardelegate/starrating.cpp 1 + + The preferred size is just enough to paint the maximum number of + stars. The function is called by both \c StarDelegate::sizeHint() + and \c StarEditor::sizeHint(). + + \section1 The \c main() Function + + Here's the program's \c main() function: + + \snippet itemviews/stardelegate/main.cpp 5 + + The \c main() function creates a QTableWidget and sets a \c + StarDelegate on it. \l{QAbstractItemView::}{DoubleClicked} and + \l{QAbstractItemView::}{SelectedClicked} are set as + \l{QAbstractItemView::editTriggers()}{edit triggers}, so that the + editor is opened with a single click when the star rating item is + selected. + + The \c populateTableWidget() function fills the QTableWidget with + data: + + \snippet itemviews/stardelegate/main.cpp 0 + \snippet itemviews/stardelegate/main.cpp 1 + \dots + \snippet itemviews/stardelegate/main.cpp 2 + \snippet itemviews/stardelegate/main.cpp 3 + \codeline + \snippet itemviews/stardelegate/main.cpp 4 + + Notice the call to qVariantFromValue to convert a \c + StarRating to a QVariant. + + \section1 Possible Extensions and Suggestions + + There are many ways to customize Qt's \l{Model/View + Programming}{model/view framework}. The approach used in this + example is appropriate for most custom delegates and editors. + Examples of possibilities not used by the star delegate and star + editor are: + + \list + \li It is possible to open editors programmatically by calling + QAbstractItemView::edit(), instead of relying on edit + triggers. This could be use to support other edit triggers + than those offered by the QAbstractItemView::EditTrigger enum. + For example, in the Star Delegate example, hovering over an + item with the mouse might make sense as a way to pop up an + editor. + + \li By reimplementing QAbstractItemDelegate::editorEvent(), it is + possible to implement the editor directly in the delegate, + instead of creating a separate QWidget subclass. + \endlist +*/ |